Laminated fin heat sink for electronic devices

ABSTRACT

A heat sink may transfer heat from electronic devices. A heat conductive base may have integrally attached thereto a plurality of parallel fins. The fins may be made up of two sheets of material. One sheet may be a metal having significant structural integrity and the other sheet of material may be a pyrolytic graphite material having excellent heat transfer characteristics. The two layers may be integrally bonded together.

BACKGROUND

This invention relates to removing heat from heat producing electronicdevices such as microprocessors.

In operation, electronic devices, including microprocessors, tend togenerate heat. Their performance may be adversely affected by theirtemperature. Thus, it is advantageous to remove heat from the integratedcircuits as effectively as possible.

To this end, heat sinks are commonly attached to integrated circuitpackaging. These heat sinks may include fins and integrated heatspreaders which transfer heat from the integrated circuit packaging tothe heat sink.

Existing heat sinks tend to be heavy, contributing to weight of theoverall electronic device. In some electronic devices, including mobiledevices, overall weight is an important factor.

Thus, there is a need for ways to improve the heat transfer fromelectronic devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial, front elevational view of one embodiment of thepresent invention in the course of manufacture;

FIG. 2 is a partial, front elevational view of the embodiment of FIG. 1after further processing; and

FIG. 3 is a perspective view of one embodiment of the present invention.

DETAILED DESCRIPTION

Referring to FIG. 1, a heat sink base 12 may be formed of copper orother heat conducting material. The base 12 may have a number of closelyspaced fin receiving apertures 16. In one embodiment, the fin receivingapertures 16 may have a downwardly expanding, dovetail shape.

A heat sink fin 14 b may include a metallic layer 18 and a graphite ornon-metallic layer 16. The non-metallic layer 16 provides good heattransfer characteristics at relatively lower weight compared to metals.In other words, the layer 16 is lighter than the layer 18 per unit ofvolume. The layers 16 and 18 may be bonded together along the line 20.

In the illustrated embodiment, the layers 16 and 18 are of equalthickness. One of the layers 16 or 18 may be thicker in someembodiments.

In order to join the fin 14 b to the base 12, crimping forces, indicatedby the arrows A and B, may be applied in one embodiment. In other words,the heat sink fin 14 b may be inserted into the slot 16. Thereafter, thetwo opposed sides of the base 12 are compressed together causing theedges 17 to cut into and engage the material of the fin 14 b. To thisend, it may be advantageous, in some embodiments, that the material ofthe base 12 is harder than the material used for the layer 16 or 18.

Referring to FIG. 2, the completed structure may include a fin 14 aengaged in a dovetail arrangement in the base 12. Indentations 19 may beformed in the fin 14 a caused by the base material 12 crimping process.

The fins 14 may be made of a high conductivity metal and a pyrolyticgraphite material in some embodiments. The two material sheets may becompressed together and held in place with a high thermal conductivityadhesive along the bond line 20 to form a laminated fin 14. Thelaminated fin 14 may then be permanently attached to the heat sink base12, for example, using the crimping process illustrated in FIGS. 1 and2. The laminated fin 14 is used in place of the traditional solid metalfin, achieving improved thermal performance and reduction in weight insome embodiments.

The metal layer 18 provides structural integrity to the laminated fin14. An isotropic metal layer 18 may also act as a medium to transferheat to the surrounding air via forced convection, as one example. Inone embodiment, the layer 18 may be aluminum.

The layer 16, which may be graphite, may spread the heat in a moreefficient manner than metal since layer 16 may have a thermalconductivity value on the order of three times that of solid metals.Since graphite material is non-isotropic, thermal conductivity in onedirection is significantly lower than in the other two directions ofheat transfer. As a result, heat may be transferred effectively in thedirection of the fin height and length, but not so in the direction offin thickness. However, this is insignificant since the heat can stilleasily be transferred through the relatively thin fin thickness.

The layer 16 may be in intimate contact with the base 12 to improve theheat transfer through the laminated fin 14. To this end, the laminatefin 14 may be permanently attached to the base 12.

In some embodiments of the present invention, graphite material withadvantageous heat transfer properties can be used in a fin shape havingrelatively extended aspect ratios. Normally, graphite material would notbe sufficiently tough to be used in such environments. However, thecombination of graphite and metal has both advantageous heat transferproperties and sufficient structural integrity.

Referring to FIG. 3, the heat sink fins 14 may be attached to a base 12so that a large number of fins are arranged in close proximity. The fins14 may be rectangular in shape, in one embodiment, with the long axisextending along and into the base 12. An electronic device 20, such as amicroprocessor, may be thermally coupled to the base 12. In someembodiments, thermal interface materials may be utilized between thedevice 20 and the base 12. In addition, an integral heat spreader may beapplied between the electronic device 20 and the base 12. In someembodiments, the electronic device 20 may consist of an integratedcircuit enclosed within an integrated heat spreader.

In one embodiment of the present invention, the aspect (height tothickness) ratio of the fins 14 may be higher than 20:1. In oneparticularly advantageous embodiment, the aspect ratio may be 60:1.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

1. A method comprising: forming a heat transfer fin of a laminate of ametallic and a non-metallic layer, said metallic layer providingstructural integrity to the laminated fin.
 2. (canceled)
 3. The methodof claim 1 including permanently securing said fin to a heat conductivebase using crimping.
 4. The method of claim 1 including adhesivelybonding said metallic and non-metallic layers.
 5. The method of claim 1wherein forming a heat transfer fin includes forming a fin of a laminateof a metallic and a pyrolytic graphite material.
 6. The method of claim1 including forming the fin with an aspect ratio higher than 20:1. 7.The method of claim 5 including forming the fin with an aspect ratio of60:1.
 8. The method of claim 1 including securing heat transfer fin toan integrated circuit.
 9. The method of claim 8 including securing saidheat transfer fin to a microprocessor.
 10. The method of claim 2including forming the metallic and non-metallic material of equalthicknesses.
 11. A heat sink comprising: a heat sink fin includingmetallic and non-metallic materials, said metallic material providingstructural integrity to said fin; and a conductive base, said finsecured to said base.
 12. (canceled)
 13. The heat sink of claim 11wherein said fin is crimped to said base.
 14. The heat sink of claim 11wherein said metallic and non-metallic materials are adhesively bonded.15. The heat sink of claim 11 wherein said non-metallic material is apyrolytic graphite material.
 16. The heat sink of claim 11 wherein thefin aspect ratio is higher than 20:1.
 17. The heat sink of claim 16wherein the fin aspect ratio is 60:1.
 18. The heat sink of claim 11wherein said base is secured to an integrated circuit.
 19. The heat sinkof claim 18 wherein said integrated circuit is a microprocessor.
 20. Theheat sink of claim 11, said fin including a first sheet of metallicmaterial and a second sheet of non-metallic material, said sheets beinglaminated together.
 21. The heat sink of claim 20 wherein said first andsecond sheets are of equal thicknesses.
 22. An integrated circuitcomprising: an integrated circuit chip; and a heat sink secured to saidchip, said heat sink including a heat transfer fin of a laminate ofmetallic and non-metallic material, said metallic material providingstructural integrity to said fin.
 23. The circuit of claim 22 whereinsaid heat sink includes a conductive base, and said fin is crimped tosaid base.
 24. The circuit of claim 22 wherein said metallic andnon-metallic materials are adhesively bonded.
 25. The circuit of claim22 wherein said non-metallic material is a pyrolytic graphite material.26. The circuit of claim 22 wherein the fin aspect ratio is higher than20:1.
 27. The circuit of claim 26 wherein the fin aspect ratio is 60:1.28. The circuit of claim 22 wherein said heat sink includes a basesecured to said integrated circuit chip.
 29. The circuit of claim 28wherein said integrated circuit chip is a microprocessor.
 30. Thecircuit of claim 22 wherein said metallic and non-metallic material areof equal thicknesses.